1. Technical Field
The disclosure relates in general to a semiconductor device, a start-up circuit and an operating method for the same, and more particularly to a start-up circuit applied for a power supply device and an operating method for the same.
2. Description of the Related Art
In recent years, green power technique has attracted attention. It is developed with a trend towards high conversion efficiency and low standby power consumption. A HV process has been widely used for a power supply such as a switch mode power supply. A switch mode power IC is formed by integrating a start-up circuit and a PWM circuit. A conventional start-up circuit for a HV device uses a resistor for providing a charging current to a charging capacitor until a voltage on the capacitor is achieved to a starting voltage of the PWM circuit. Then, the start-up circuit stops working. However, after stopping working, the resistor of the start-up circuit still dissipate powers. Therefore, power saving effect of the device is not good. In some techniques, the start-up circuit uses a depletion-type NMOS replacing the resistor. However, as the start-up circuit is in a stopping condition, a high leakage current through the depletion-type NMOS would be easily generated due to a strong negative threshold voltage (Vt).